In some leisure vehicles, for example, motorcycles, a lubricating oil pump is typically built into a four-cycle engine to feed a lubricating oil to engine components such as journal members or slidable members (see Japanese Utility Model Application Publication No. Sho. 60-155709).
In order to clean exhaust gases emitted from engines or to gain a high engine power, some engines are equipped with a variable valve system in which a lift amount of intake and exhaust valves and a valve timing are variable according to, for example, an engine speed. An actuator for driving the variable valve system is typically driven by an oil pressure of the lubricating oil of the engine which is fed from the lubricating oil pump.
However, the lubricating oil used to drive the actuator for driving the variable valve system may be degraded or may be diluted by a fuel (gasoline) flowing into an interior of a crankcase through a gap between a piston and a cylinder.
Conventionally, an electric motor is sometimes used to operate a throttle valve, a clutch, etc., by a “fly by wire” system. In this case, in order to operate the throttle valve, etc., quickly, the electric motor is required to generate a high output power. While the electric motor consumes a relatively high amount of electric power, a leisure vehicle such as a motorcycle has a limited electric capacity, in contrast to automobiles or trucks in general. If a large battery and a corresponding generator are equipped in a leisure vehicle, then the weight of the leisure vehicle increases. This is problematic, because light handling is desired during travel of the leisure vehicle.